Method for the production of levulinic acid and its derivatives

ABSTRACT

A method of producing dehydration products from one more 5-carbon or 6-carbon sugars includes reacting said one or more sugars at 40-240° C. for 1 to 96 hours in the presence of 5-90% sulfuric acid, separating the reaction products, and recovering levulinic acid. The sugars are can be generated from strong acid hydrolysis of biomass, such as rice straw, paper, cotton and other cellulosic materials.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/747,441, filed Nov. 8, 1996 now U.S. Pat. No. 5,892,107.

FIELD OF THE INVENTION

The present invention relates to a method of producing levulinic acidfrom sugars in the presence of concentrated acid. In addition, theinvention relates to a method for producing methytetrahydrofuran fromthe levulinic acid thus obtained. These novel methods can utilize wastebiomass as the starting material for the levulinic acid and its numerousderivatives, thus adding to the economic viability of the invention.

BACKGROUND OF THE INVENTION

Levulinic acid is a major product of the controlled degradation ofsugars by acid hydrolysis. Although levulinic acid has been known sincethe 1870's, it has never attained much commercial significance. One ofthe reasons for its slow development is the cost of the raw materialsfor synthesis. Another reason is the low yields of levulinic acidobtained from most synthetic methods. These low yields are largely dueto the inherent physical properties of levulinic acid which do not allowfor its facile recovery. Moreover, the production of levulinic acid hashad high associated equipment costs. Given these factors, therefore, theproduction of levulinic acid has not appeared to be commerciallyfeasible.

Despite the inherent problems in the production of levulinic acid,however, the reactive nature of levulinic acid makes it an idealintermediate leading to the production of numerous useful derivatives.Levulinic acid, therefore, is desirable as a basic chemical rawmaterial. See R. H. Leonard, "Levulinic Acid as a Basic Chemical RawMaterial, " Industrial and Engineering Chemistry, Vol. 48, p.1331-41(1956).

The formation of levulinic acid from low-cost cellulosic material could,however, overcome one of the major difficulties encountered in othersynthetic processes. By starting with waste biomass the cost of thestarting material for production of levulinic can be greatly reduced.Moreover, the supply of sugars from cellulose-containing plant biomassis immense and replenishable. Most plants contain cellulose in theircell wall. For example, cotton is 90% cellulose.

Furthermore, it has been estimated that roughly 75% of the approximate24 million tons of biomass generated on cultivated lands and grasslandsis waste. This cellulose that is derived from plant biomass could be asuitable source of sugars to be used in the process of obtaininglevulinic acid. Thus, the conversion of such waste material into auseful chemical, such as levulinic acid, would be desirable.

Sugars are converted to levulinic acid essentially by a process ofdehydration and cleavage of a mole of formic acid. See Reid H. Leonard,supra. The literature in the art suggest that levulinic acid can beformed quite readily from glucose and other sugars by the action ofboiling the sugars in a dilute acid solution. See P. T. Sah and S. -Y.Ma, "Levulinic Acid And Its Esters," J. Amer. Chem. Soc., 52:4880(1930); and L. Fieser and M. Fieser, "Reagents for Organic Synthesis,"John Wiley and Sons, Inc. 1967, p. 564-66.

In the literature concerning production of levulinic acid from sugars,however, generally HCl is used as the acid source in the dehydrationreaction of sugars. See L. Fieser and M. Fieser, supra.; Alva Thompson,U.S. Pat. No. 2,206,311; Wendell W. Moyer, U.S. Pat. No. 2,270,328;Georg Scheuing and Wilhelm Konz, U.S. Pat. No. 2,305,738; Walter N.Haworth and Leslie F. Wiggins, British Patent No. 583,533. Sulfuric acidhas been used as the acid source in dehydration reaction of bran, thehere the reported product is furfural, rather than levulinic acid. SeePaul Karrer, "Organic Chemistry," 2nd ed, Elsevier Publishing Co, Inc.,New York 1946, p.737.

The theoretical yield of levulinic acid from a hexose is 64.5%. Theliterature in the art, however, indicates that only about two-thirds thetheoretical yield can be attained in the presence of dilute HCL.Interestingly, substantially the same yields were obtained fromcellulose in Douglas fir sawdust. See Reid H. Leonard, supra. Thus, itappears possible to utilize cellulosic materials to produce sufficientquantities of levulinic acid to be used as a basic raw chemicalmaterial.

If a low-cost production of levulinic acid could be achieved, such asthe formation of levulinic acid from low-cost cellulosic material, theuseful derivatives of this chemical are numerous. For example, esters oflevulinic acid are used for flavoring, and some have been reported to beused as plasticizer. Reaction of levulinic acid with carbonyl reagentsalso can yield numerous derivatives, many of which are hydrazones andsemicarbazones. These derivatives are of interest for conversion intopyridaziones and for the preparation of soluble derivatives ofinsoluble, but biologically active, materials. Also alkyl metal halidesreact with levulinate esters to yield a series of γ-substitutedγ-valerolactones, some of which may be used for perfumes and flavors.

Oxidation products of levulinic acid are also known. These include theperoxide, methyl vinyl ketone, and succinic, malonic, and acetoacrylicacids. These derivatives have been postulated to be of use in foods, andas solvents in liquid-liquid extractions of hydrocarbons. In addition,the 4-amino derivatives of levulinic acid readily forms lactams and5-methylpyrrolidones, while the amides upon hydrogenation of the ketogroup, also form 5-methylpyrrolidones.

Upon distillation, dehydration of levulinic acid occurs and α-angelicalactone (γ-lactone of 4-hydroxy-3-pentenoic acid) is formed togetherwith some β-angelicalactone (γ lactone of 4-hydroxy-2-pentenoic acid).Various heterocyclic compound are also derived from levulinic acid. Someof these are pyrones, dioxanes, a coumarin, and thiazocines, which havebeen proposed for use as bacteriostatic and analgesic agents.

Moreover, substitution of levulinic acid for a portion of the acetylgroups in vinyl acetate-containing resins and cellulose acetate has beenshown to yield materials of increased strength. The α-angelica lactones,one of the simplest products to be made from levulinic acid, can also beconverted to a series of pseudolevulinic acid derivatives and has alsobeen reported to be a means of obtaining 3-chloro-levulinic acid.

Reduction products of levulinic acid are also important. It has beenreported that catalytic hydrogenation at temperatures above 200° C.yields substantial amounts of 1,4-pentanediol, and smaller amounts ofα-methyltetrahydrofuran, and 1-pentanol. See Reid H. Leonard; G. Natta,R. Rigamonti and E. Beati, "The Hydrogenation of 2-furaldehyde And ItsDerivatives," Chimica e Industria (Italy) 23, 117-23 (1941).

In all, the exceptional reactivity of levulinic acid and its lactonescoupled with its availability from waste biomass provide an ideal set ofconditions for the use of levulinic acid as a basic chemical rawmaterial. Thus, there exists a need to be able to produce levulinicacid. Moreover, it would be most desirable to be able to producelevulinic acid in an economically viable and environmentally safeprocess.

SUMMARY OF THE INVENTION

The present invention is directed toward a method of producing levulinicacid and other derivatives, such as furfural, 5-HMF, succinic acid,maleic acid, fumaric acid, and methyltetrahydrofuran, from sugars.

In one aspect of the present invention, levulinic acid is produced byutilization of sugars produced by strong acid hydrolysis. The steps ofthis method include: 1) mixing biomass containing cellulose andhemicellulose with a solution of approximately 5-50% acid, preferably10-30% acid, thereby decrystallizing the biomass, 2) heating the mixtureto about 80-200° C., preferably 110-160° C., for 1 to 30 hours,preferably 2 to 10 hours, thereby hydrolyzing the cellulose andhemicellulose materials and causing the reaction of the resultingmixture of sugars to form the reaction products, 3) pressing orfiltering to separating the liquid portions from the solid biomassportion, 4) separating the reaction products, and 5) recoveringlevulinic acid. It is noted that sulfuric acid is the preferred acid tobe used in this method, and that the biomass used in the start of thereaction leading to levulinic acid can consist of rice straw, woodyplant, paper, cotton, corn stalks, grass, bagasse, or other plantmaterial. Both cellulose and hemicellulose can also be used as startingmaterial when utilizing the method outlined above.

Preferably the above method is performed wherein the concentrations ofthe cellulose (within the preferred range of 12-39% percent by weight inthe reaction solution) and acid (in percent by weight in the reactionsolution) and the temperature are chosen according to the relation:

    A=-0.4T30 70-0.59(C-25.5)

wherein A is the concentration of sulfuric acid, T is the temperature indegrees Celsius, and C is the concentration of cellulose, wherein thevalue of A may deviate from the valve obtained from the equation by plusor minus 5% by weight in the reaction solution, the values of T maydeviate by plus or minus 10° C. of the values obtained from theequation, and the values of C may deviate from the value obtained fromthe equation by plus or minus 5% by weight in the reaction solution.Preferably, the biomass concentration is 20-40%, more preferably 30%.

The production of levulinic acid via the above process also allows forrecovery of products selected from the group consisting of furfural,5-HMF, succinic acid, maleic acid, fumaric acid. These products alongwith levulinic acid and sulfuric acid can be separated bychromatography, preferably using an ionic resin. However, it is morepreferred that the separation be effectuated using an anionic resin, andmost preferably the resins would also consist of multiplechromatographic columns.

In another aspect of the present invention, the levulinic acid obtainedfrom either of the three methods outlined above can be used to formderivative products, such as methyltetrahydrofuran. The steps of thismethod include: 1) hydrogenation of the levulinic acid in the presenceof H₂ and a metal catalyst, 2) separating the reaction products, and 3)recovering methyltetrahydrofuran. This hydrogenation reaction can alsobe conducted in the presence of added ethanol, either in a wet or in adry form. The methyltetrahydrofuran product can be dried after thehydrogenation reaction, leaving the resulting product in a dry blendform. The preferred metal catalyst to be used in the hydrogenationreaction of levulinic acid is a Ni/Co catalyst. Also, it should be notedthat if the levulinic acid is dried subsequent to its production, theresultant product is angelica lactone, due to dehydration of thelevulinic acid.

In utilizing the above-outlined method of producing levulinic acid, itis preferred that the reaction products be filtered prior to separation.Additionally, it is preferable that the filter be washed one or twotimes, and that preferably these washes are to be combined prior toseparation. Moreover, following separation of the reaction products,levulinic acid can be concentrated to facilitate any further reaction.

In yet another aspect of the present invention, when utilizing theabove-outlined method, an alcohol can be added to the reaction mixturesubsequent to the production of levulinic acid. The resultant reactionmixture is preferably run for 1-10 hours at the reaction temperature ofthe alcohol. The final reaction mixture can be separated to yieldlevulinate ester. Preferably the reaction time to produce the esterwould be 2-8 hours with a reaction time of 3-6 hours being mostpreferred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic view of the method of the present inventionillustrating in a Product Flow Diagram the steps leading to theproduction of levulinic acid and tetramethyhydrofuran.

FIG. 2 represents the relative refractive index of the products as afunction of time of elution from the chromatographic system.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

Recently, a successful process has been discovered that provides forstrong acid hydrolysis of plant biomass consisting largely of cellulosicand hemicellulosic materials. See U.S. Pat. No. 5,526,777 ('777 patent),entitled "Method of Producing Sugars Using Strong Acid Hydrolysis ofCellulosic and Hemicellulosic Materials," and hereby incorporated bythis reference thereto. This acid hydrolysis method results in a highyield of sugars as an intermediate in the process. Moreover, this acidhydrolysis process provides a means for producing sugars from biomass ina manner that reduces the amount of waste product of effluents produced.

Thus, the process of the '777 patent is designed to reuse all aqueousstreams and to convert all solids to saleable or useful products. Muchof the acid used is also recovered for recycling. Also where the biomasscontains high levels of silica, the process is able to produce silicagel, sodium silicate, potassium silicate, zeolites, or other ancillaryproducts. Moreover, a high yield of sugar is obtained form thehydrolysis of the biomass, making concentration of the sugar streamsunnecessary for most subsequent processes.

Other features of the patented acid hydrolysis method contribute to itsefficiency and economic feasibility in the production of sugars. Theseinclude the use of atmospheric pressure and relatively low temperatures.Moreover, the process does not involve the production of furfural andsimilar undesirable by-products which are toxic and also may inhibitsubsequent reactions of the sugars thus obtained. Finally, this processdoes not require the use of exotic and expensive materials ofconstruction such as tantalum steel.

Thus, the process of the '777 patent provides an efficient,cost-effective means of producing useful chemicals from the hydrolysisof agricultural waste, while at the same time producing little or notwaste effluents or materials. Moreover, since the hydrolysis processproduces a high yield of sugars, it would appear to be a suitable methodfor use in the production of useful derivatives from the sugarintermediate thus obtained. One such derivative could be levulinic acid.

The present invention provides an improved process for obtaininglevulinic acid from sugar, as well as derivatives of levulinic acid,such as methyltetrahydrofuran(MTHF). Levulinic acid can be produced fromsugars derived from cellulose and hemicellulosic materials, as detailedin the '777 patent and incorporated herein by reference, or from sugarsderived from other sources. It should be noted, however, that althoughthe strong acid hydrolysis process described in the '777 patent,provides an efficient means of producing sugars from biomass to be usedsubsequently in the method of the present invention, this methodrepresents only one route to obtain raw sugar to be used as startingmaterial in the disclosed invention. The novel method of the presentinvention leading to levulinic acid can utilize any sugar component as astarting material, regardless of whether the sugar is mixed, acombination of 5-carbon and 6-carbon sugars, exclusively contains5-carbon or 6-carbon sugars, or is obtained from biomass by methodsother than that described in the '777 patent.

If the method detailed in the '777 patent is utilized to obtain sugar,the hydrolysate will generally include the 6-carbon sugars (C6) glucose,mannose and galactose and the 5-carbon sugars (C5) xylose and arabinose.The hydrolysate mixtures formed in the method of the '777 patentprimarily consist of glucose and xylose with small amounts of the othersugars. However, where cellulose is used as the starting material in theprocess, such as that of recycled paper, the exclusive product isglucose. Additionally, in situations where the biomass has increasingamounts of hemicellulose, the entire range of C6 and C5 sugars isproduced.

The present invention discloses a novel method to produce dehydrationproducts of sugars, such as levulinic acid (LA), furfural,5-hydroxymethyl-2-furanone (5-HMF), maleic acid (MA), succinic acid(SA), and fumaric acid (FA), even if the starting components consist ofmixed sugars. The present invention also allows for the selection ofconditions that can alter the product ratio so that economic flexibilitycan be incorporated into the production of these dehydration products.

In addition, the method of the disclosed invention provides steps toprepare high yields of the dehydration products and to prepare theproducts that all process streams are reusable, after the recovery ofthe desired products. Moreover, the present invention allows for thesedehydration products to be produced in high yield in economically viableand environmentally safe processes. Finally, the invention alsodiscloses the method of preparation of derivatives of levulinic acid byhydrogenation yielding methyltetrahydrofuran (MTHF).

There are numerous advantages to the present invention. These includethe following:

1. A mixed C6-C5 acid stream can be used without the need for separatingthe sugars;

2. The yields of levulinic acid and its derivative, MTHF, aresignificantly higher than other known methods, in part due to the highconcentration of sulfuric acid which was discovered to act as adehydration catalyst at the concentrations utilized in the presentinvention;

3. The concentration of sulfuric acid remains high throughout thereaction and subsequent separation, thus facilitating its recovery forreuse;

4. The product mix can include products which become intermediates tothe common final product;

5. The invention allows for the recycle and reuse of all streams, andany unwanted byproducts can be subsequently oxidized to non-toxicmaterials.

This last advantageous aspect of the invention is significant whensulfuric acid is used in the process because the presence of this acidwill degrade and oxidize products if not removed. For example, H₂ SO₄degrades formic acid, which is formed as a necessary by-product in thedehydration reactions.

FIG. 1 shows a Product Flow Diagram indicating the overall steps leadingto the production of levulinic acid and/or MTHF. This Product FlowDiagram is illustrative of a preferred embodiment. All streams areindicated by arrows with the overall steps being illustrated by thelarger boxes to which the product streams are directed.

First the sugar (1) is fed into the reactor (2). The sugar can bederived from the process of strong acid hydrolysis, as detailed in the'777 patent, or can be any sugar, either a mixed sugar, consisting ofboth 6-carbon and 5-carbon sugars, or exclusively a 6-carbon or 5-carbonsugar. Next the reaction mixture is heated at 80-120° C. for 7 to 42hours. Preferably the reaction of the sugars in concentrated sulfuricacid is carried out at 100° C. for 24 hrs. When the method detailed inthe '777 patent is used, the concentration of sulfuric acid will be inthe range of 25-39%, without further addition of acid. If the sugarsource is not from that of the strong acid hydrolysis method, however,sulfuric acid is added to the reactor to a final concentration ofapproximately 30-39%.

Next the resulting product mixture (3) is transferred to a filtrationsystem (4), where an initial cake (5) is formed. The first filtrate (6)is then transferred to the holding tank (7). The cake is subsequentlywashed with H₂ O (8), resulting in a second filtrate (9) which is alsotransferred to the holding tank. After the H₂ O wash, the cake discharge(10) can be removed from the filter.

The combined filtrates (11) are then applied to the chromatographicseparator (12), where the products of the reaction as well as sulfuricacid can be separated. The products are separated by H₂ O (13) feed intothe separator. Preferably the resin utilized in the chromatography is ananionic resin, for which sulfate ions form the anionic state. Mostpreferably, a system of multiple chromatographic columns, referred to inthe art as "simulated moving bed chromatography," can be utilized toeffect the initial separation; the use of multiple chromatographiccolumns permits the removal of products, addition of further eluents, orrecycles between columns.

FIG. 2 shows a typical chromatograph of the separation after reactionfor 24 hrs at 100° C., where levulinic acid is the primary product. Thischromatograph was generated using a Dynamax™ NH₂ 83-701-C column, whichis provided prepacked with a weak anion amine resin and is availablefrom Rainin of Woburn, Mass. As FIG. 2 illustrates, sulfuric acid can becleanly separated from the levulinic acid product. This allows thestrong acid to be recycled for reuse, and thus, adding to the economicviability of the process. Under these conditions, succinic, maleic andfumaric acid can also be separated.

The following sets forth one exemplary set of specific separationconditions:

A 24" long, 2" in diameter column was loaded with Mitsubishi A306Sanionic resin to a bed volume of 1 liter. 75 ml of levulinicacid/sulfuric acid mixture (5% levulinic acid and 30% H₂ SO₄) was fedonto the column and eluted with H₂ O. Levulinic acid eluted from thecolumn after approximately 24.5 minutes with the sulfuric acid elutingat approximately 28 minutes. With an application of only 50 ml, thelevulinic acid still eluted at approximately 24.5 minutes, while thesulfuric acid eluted at approximately 29.75 minutes. It is importantthat these separation condition yield enough of a difference in theelution profile of the products to be utilized on a moving bedcommercial chromatographic separation system. Moreover, it appears thatthe separation can proceed using a cationic resin as well.

Another example of a particular separation procedure is as follows:

A 24" long, 2" in diameter column was loaded with Dow XFS-43254.00 anionresin to a bed volume of 1 liter. 100 ml of levulinic acidisulfuric acid(5% levulinic acid and 30% H₂ SO₄, was fed to the column eluted with H₂O. Levulinic acid eluted at approximately 22.75 minutes, and thesulfuric acid eluted at approximately 40 mintues. In this example, therewas total separation, with no overlap of the peaks, thus indicating thatthis procedure could be used to give an effective separation even in theabsence of simulated moving bed techniques. However, the moving bedchromatographic techniques are preferred because higher concentrationscould be maintained throughout the separation.

Following the chromatographic separation, sulfuric acid (14) is feedinto an acid concentrator (15) leading to the removal of H₂ O (16) andconcentrated H₂ SO₄ (17) being available for reuse at the initial stageof the strong acid hydrolysis process. Furfural (18), along with 5-HMF,can also be separated by the chromatography method described above,eluting from the column after the sulfuric acid component of thereaction mixture. The furfural containing eluent can then be furtherconcentrated and purified (19), leading to furfural product (20) and H₂O (21).

The final eluent from the chromatographic separator is levulinic acid(22) in H₂ O with a small amount of acid. The product can be furtherconcentrated (23) by evaporation of H₂ O (24) prior to the hydrogenationreaction, leaving levulinic acid product containing a small amount ofacid. Advantageously, the acid present serves as a catalyst, thusobviating the need to add acid at this point. Once the H₂ O is removed,the temperature is increased to 150° C., and a vacuum is applied at 10torr. Thus, various forms of isomers of angelica lactone (25) can beformed, which can be collected and used in the hydrogenation reaction.

One use of the levulinic acid obtained is to hydrogenate the product toMTHF. If MTHF is desired as an end product, angelica lactone isomers aretransferred to the hydrogenator (26), along with H₂ (27), ethanol (28),and the Ni/Co catalyst (29). This mixture is reacted in thehydrogenation reactor at a pressure of 750-3000 psig, until there is noremaining H₂ uptake. Preferably, the temperature of the reaction wouldbe at 50° C. to at temperature below the decomposition temperature ofthe lactone, which is approximately at 200° C. The product, MTHF (30),can then be transferred to a liquid or vapor phase dryer unit to removeH₂ O (31), also making using of a desiccant or absorbent. The final MTHFproduct is now in a dry blend form (32). Moreover, the production of amixed stream in this case, that is MTHF and ethanol, would have anadvantage over current technology in the finished mixtures can be mademore economically than making the products separately, and then blendingthe finished products for use.

It should also be noted that in many instances it is more economicallysound to insert an separation step in the midst of the levulinicformation at the site of the primary reactor, so that product of valuecan be immediately extracted. Thus, it may be undesirable to wait 7-42hours to extract the products. For example, in this dehydrationreaction, as time proceeds furfural is converted into succinic, maleic,and fumaric acids. If furfural was a desired product, it would bepreferred to do an initial separation early in the reaction, and then,sending the remainder back to the reactor for completion of thelevulinic acid reaction.

It is noteworthy that the dehydration reaction produces differentproducts as the time of reaction is increased. At 100° C., the reactionof the 6-carbon sugars will go through 5-HMF yielding levulinic acid,whereas the reaction of 5-carbon sugars will go through furfural toyield succinic, maleic, and fumaric acids. However, literature in theart indicate that these reactions may not be exclusive, in that aintermediate product of the reaction with 6-carbon sugars may be a5-carbon sugar production, and vice versus. Ojota et al. J. Pharm.Pharmac., 30:668 (1978). In addition, Great Lakes Chemical have achemical process of making MTHF from furfural alcohol, by starting with5-carbon sugars and resulting in furfural.

Moreover, it is generally hypothesized that the synthesis of levulinicacid requires the simultaneous oxidation of aldehydes, as a source ofhydrogen, resulting a reduced form of levulinic acid. Thus, if mixedsugars are used in the reaction, the overall yields can be improvedbecause the degradation products of the 5-carbon sugars, for example,the aldehydes produced, act as appropriate reducing agents for thereaction, leading to higher yields of levulinic acid from the 6-carbonsugars.

Although it is possible to write a balanced equation for the reaction ofa 6-carbon sugar leading to one mole of levulinic acid, one mole offormic acid, and one mole of H₂ O, the actual reaction mechanism is notcompletely known. The requirement of a saturated levulinic acid product,plus the unsaturated nature of 5-HMF, however, indicate that it ishighly probable that more than one mole of 6-carbon sugar is required toyield a mole of levulinic acid. For example, Augh et al. showedpolymerization of 5-HMF, thus reducing levulinic acid. Thus, thetheoretical yield of 64% dictated by the simple balanced equation isnever achieved. The reported yields are generally on the order of 20% ofthe theoretical yield, i.e. a yield of about 13%. There are only a fewreported results; in one report, 150 g of product resulted from reactionof 1000 g of glucose with HCl, i.e. a 15% yield. This result was claimedto be an improvement over previous reported results. See Sah et al.,supra.

In the present invention the actual yield of levulinic acid for the 7hour reaction time was 23.3%, or 36% of the theoretical yield. Thisyield is approximately 50% higher than the reported literature value.See L. Fieser and M. Fieser, "Reagents for Organic Synthesis," JohnWiley and Sons, Inc. 1967, p. 564-66. It is noteworthy that the 24 hourreaction yields approximately twice the reported yields.

Finally, analysis of the method of the present invention, indicate thatall the sugar disappears from the reaction mixture between 7-24 hoursafter the reaction is initiated. These results also show an increase in5-HMF as a function of decrease of the sugar levels in the reactionmixture. Levulinic acid is produced following the appearance of 5-HMF.

When the sugars from which the levulinic acid is produced are derivedfrom cellulosic and hemicellulosic raw materials, the method describedabove results in the highest yield of product per pound of raw material.If, however, economic factors favor a process which is faster andrequires less capital investment, an alternate method, described below,which is faster and requires fewer steps may be used. This alternateprocedure is an integrated method wherein the sugar or sugar/acid streamis not recovered as an intermediate, and results in a slightly loweryield of levulinic acid per pound of raw material than that describedabove, but the yields are still higher than the previously reportedliterature values for yields.

The integrated procedure begins by mixing cellulosic and hemicellulosicraw materials, such as biomass or recycled paper, with acid, preferablysulfuric acid to form the reaction solution. The preferredconcentrations of the components, as percent by weight in the reactionsolution, are preferably about 20-40%, more preferably about 30% for thebiomass; preferably 12-39%, more preferably 21-30% for the cellulose;and preferably 5-50%, more preferably 10-30% for the acid. When the acidand biomass are combined, decrystallization of the biomass occurs. Thedecrystallization is exothermic, so the temperature spontaneously risesas the components are mixed. The temperature should not be allowed torise higher than about 40-60° C., otherwise the materials may degradebefore significant conversion takes place. A reasonable temperature canbe maintained by controlled addition of the raw materials or cooling thesolution.

Once the decrystallization has taken place, the reactants are heated to80-200° C., preferably 110-160° C., for a time of 1 to 30 hours,preferably 2 to 10 hours. Unlike the longer method described previouslywherein the hydrolysis and reaction of the sugars are performedseparately, in this method as the decrystallized materials hydrolyze toform sugars those sugars then react to form levulinic acid. Furthermore,all of this is done while the solution is in contact with the remainingsolids. Once the reaction is complete, the resulting product mixture isprocessed according to the Product Flow Diagram beginning at step (3)and as described above.

The inventors have found that for a given amount of biomass in thereaction solution, if the temperature of the reaction is increased, theconcentration of sulfuric acid must be decreased in order to maintain ahigh yield of levulinic acid. Similarly, if the temperature of thereaction is decreased, the concentration of sulfuric acid must beincreased in order to maintain the high yield of levulinic acid. Throughexperimentation using paper as the biomass, the inventors found that therelationship between the concentration of sulfuric acid, concentrationof cellulose, and the temperature may be approximated by the equation:

    A=-0.4T+70-0.59(C-25.5).

wherein A is the percent sulfuric acid by weight in the reactionsolution, T is the temperature in degrees Celsius, and C is the percentcellulose by weight in the reaction solution, which is preferably withinthe preferred range of 12-39% by weight in the reaction solution.

The series of reactions from which the equation was derived hadconcentrations of paper (85% cellulose) of 30% paper (25.5% cellulose)and 40% paper (34% cellulose) by weight in the reaction solution. Thesereactions also had sulfuric acid concentrations between 7.5% and 30% byweight in the reaction solution, and a temperature range of 110-160° C.

The equation given above approximates the conditions for achieving ahigh yield. The conditions used should deviate from those obtained fromthe equation by not more than 5% by weight in the reaction solution forthe values obtained for A, not more than 5% by weight in the reactionsolution for the values obtained for C, and not more than 10° C. of thevalues obtained for T. Greater deviations will likely result in either alower yield or a slower reaction. For the deviations for A and C, if thevalue obtained from the equation is 20, meaning 20% by weight in thereaction solution, the conditions used should lie within the range of 15and 25% by weight in the reaction solution. The results from one of theexperiments using 25.5% cellulose (30% paper) from which the aboveequation was derived is shown in Table 1 below. The percent levulinicacid (% LA) values correspond to the molar percent conversion oflevulinic acid compared to the theoretical conversion, which in the caseof conversion of cellulose to levulinic acid is 71.5%.

                  TABLE 1                                                         ______________________________________                                        REACTION CONDITIONS AND RESULTS                                                 FOR 25.5% CELLULOSE FROM PAPER                                                Acid                                                                          Con-                                                                          cent-                                                                         ra- Temperature (° C.)                                                         tion 160  150    140    130    120    110                           ______________________________________                                        30%         16.4% LA               47.1% LA                                                                             29.6% LA                                3 hrs   4 hrs 6 hrs                                                         25%  28.0% LA  32.9% LA 56.1% LA                                                6 hrs  9 hrs 9 hrs                                                          20%   40.5% LA 45.0% LA                                                          4 hrs 3 hrs                                                                15%  47.3% LA 45.5% LA 37.3% LA                                                 3 hrs 5 hrs 6 hrs                                                           10%  59.8% LA                                                                   8 hrs                                                                       7.5%                                                                        ______________________________________                                    

The reactions having a concentration of cellulose of about 25.5% byweight were generally found to than those having the concentration ofcellulose at 34%. This may be seen by the results presented in 2 below.In Table 2, as in Table 1 above, the percent levulinic acid (% LA)values correspond to the molar percent conversion of levulinic acidcompared to the theoretical conversion.

                  TABLE 2                                                         ______________________________________                                        CONDITIONS AND RESULTS                                                          USING PAPER AS BIOMASS                                                        %                % sulfuric                                                   paper % cellulose acid temperature time (hrs) yield (% LA)                  ______________________________________                                        30   25.5      10       150     8      59.8                                     30 25.5 15 150 3 47.3                                                         30 25.5 15 140 5 45.5                                                         40 34 10 150 4 33.7                                                           40 34 15 150 6 38.2                                                           40 34 15 140 4 43.6                                                         ______________________________________                                    

A Method of Production of Levulinic Acid and Other Dehydration Productsof Sugars Derived From Strong Acid Hydrolysis

A method of strong acid hydrolysis of cellulose and hemicellulose isdetailed in the '777 patent. This is a preferred method to derive sugarsas starting material for the production of levulinic acid and itsderivatives, as disclosed in the present invention. In the followingexamples, the hydrolysate was generally derived from rice straw. Inaddition, to present examples that illustrate the reaction under varyingconditions, 5-carbon and 6-carbon sugar were added to modify the ratiopresent in the hydrolysate.

After the conventional hydrolysis step of the '777 patent, there are twopoints in this process where chemistry can be performed. Moreover,either the mixed sugar stream, which is the first hydrolysis stream, orsecond hydrolysis stream consisting of virtually all glucose can beselected for use in subsequent chemical reactions. (See FIG. 1 of the'777 patent). Of course, these two streams can be combined yieldingmixed sugars as starting material in further reactions.

The two points in the acid hydrolysis process where additional chemistrycan be performed are: 1) immediately after the belt pressing step (SeeFIG. 1 of the '777 patent) or 2) immediately after the acid/sugarseparator step, where sulfuric acid is removed from the sugar residue(See FIG. 2 of the '777 patent).

After Pressing

After the first hydrolysis step, the sugar concentration isapproximately 15%, while the acid concentration is approximately 30%. Itis this stage of the strong acid hydrolysis process that appears to beideal for optimization of dehydration reactions leading to levulinicacid, furfural, 5-HMF, and other degradation products of these primaryproducts, succinic, maleic and fumaric acids. Following the reaction ofthe sugar/acid mixture, leading to the desired product(s), the productscan be separated from the acid component via chromatography, asdescribed in the above Product Flow Diagram.

The advantage of proceeding via this route is that the strong acidhydrolysis method produces sugars in high yields in a convenient part ofthe raw material concentration scheme, as described in the '777 patent.Another advantage is that reactions can be carried out with only minimalpurification of intermediates products. Thus, final purification can bedone later in the regime after products of high value have beenobtained.

It was also discovered by experimentation that sulfuric acid does notproceed via same the mechanism as HCl, which is the acid generally usedin the art to produce dehydration products of sugars, such as levulinicacid. An original experiment was performed where a solution of 10%glucose, by weight, was reacted in the presence of 1%, by weight, for 24hours at 100° C., as described in the literature. See P. T. Sah and S.-Y. Ma, "Levulinic Acid And Its Esters," J. Amer. Chem. Soc., 52, 4880(1930); L. Fieser and M. Fieser, "Reagents for Organic Synthesis," JohnWiley and Sons, Inc. 1967, p. 564-66. After essentially followingliterature reaction conditions, except that H₂ SO₄ was used instead ofHCl, there was virtually no sugar degradation and no production oflevulinic acid.

A similar reaction was also performed in which a solution of 3% H₂ SO₄and 10% glucose was reacted at 100° C. for 24 hours. In this case, theglucose decreased to 7.34% with a significant production of 5-HMF, butonly insignificant amounts of levulinic acid. Here 0.058% of levulinicacid was produced, in sharp contrast to the reported yields in thepresence of HCl. It should be noted that in substituting H₂ SO₄ for HCl,the difference in acidic value of each acid was taken intoconsideration. Thus, a 6% solution of HCl is approximately equivalent toa 3% solution of H₂ SO₄. These unanticipated results indicate that themechanism of acid action is different with H₂ SO₄ rather than HCl.Moreover, these surprising data lend support to use of the hydrolysategenerated in the strong acid hydrolysis method of the '777 patent. Theadvantage of using this hydrolysate are many. It is produced at highconcentrations in the first part of the '777 method, it contains highconcentrations of H₂ SO₄ which are necessary to get significantquantities of levulinic acid, or other dehydration products, andfinally, purification steps are eliminated until the desired productsare obtained.

EXAMPLE 1 Production of Levulinic Acid

A mixture of 5-carbon sugars, primarily xylose, 6-carbon sugars,primarily glucose, and H₂ SO₄ were reacted in H₂ O. The concentration ofmixed sugars was 10-22%, by weight, the inorganic acid was 25-39% byweight, with the remainder being H₂ O. This sugar mixture was preparedby the strong acid hydrolysis method by:

1) mixing materials cellulose and hemicellulose with a solution ofapproximately 25-90% of H₂ SO₄, by weight, thereby at least partiallydecrystallizing the biomass and forming a gel that includes a solid andliquid portion;

2) diluting the gel thus obtained to an acid concentration ofapproximately 20-30% by weight and heating the gel to about 80-100° C.,thereby hydrolyzing the cellulose and hemicellulose materials (firsthydrolysis step);

3) separating the liquid portion from the solid portion, therebyobtaining a first liquid containing a sugar/acid mixture;

4) mixing the separated solid portion with a solution of about 25-90% H₂SO₄ by weight until the acid concentration of the resulting gel isbetween 20-30%, by weight, and then heating the mixture to temperatureof 80-100° C., thereby further hydrolyzing the cellulose andhemicellulose materials remaining in the separated solid portion (secondhydrolysis step);

5) separating the resultant liquid portion form the solid portion, andthereby obtaining a second liquid containing a sugars/acid mixture;

6) combining the first and second liquids.

The above liquid mixture is then heated at approximately 80-120° C. forabout 7-42 hours, depending on the product ratio desired. It ispreferable, however, that the reaction temperature be approximately 100°C. The dehydration products formed are levulinic acid, 5-HMF, furfural,succinic acid, maleic acid, and fumaric acid.

The product stream is then separated into component liquid streamscontaining the desired combination of products, or the individualproducts, and a separate stream which contains the inorganic acid, asillustrated in the Product Flow Diagram. The organic product streamseach contain less that 3% sulfuric acid, and the inorganic streamcontains less than 3% organic product. The inorganic stream can beconcentrated to facilitate reuse of the sulfuric acid.

The organic products are further purified by conventional meansresulting in the removal of H₂ O, inorganic acid and minor impurities.For example, furfural is purified by a second distillation, whichfollows azeotropic distillation of the furfural/H₂ O mixture. Levulinicacid can be further purified by first by distilling the product followedby vacuum distillation. If necessary, recrystallization of the levulinicacid product can also be performed.

EXAMPLE 2 Production of Levulinic Acid

A mixture of 5-carbon sugars, primarily xylose, 6-carbon sugars,primarily glucose, and H₂ SO₄ were reacted in H₂ O. The reactionconditions consist of heating the mixture at a temperature of 80-120° C.for 7-42 hours, depending on the desired product ratio of levulinicacid, 5-HMF, furfural, maleic acid, succinic acid and fumaric acid.Preferably the reaction would proceed at 100° C. for 24 hrs. Theconcentration of mixed sugars were 10-22%, by weight, the inorganic acidwas 25-39% by weight, with the remainder being H₂ O. After production ofthe dehydration products, the reaction mixture is separated and purifiedas described in the Product Flow Diagram of FIG. 1. This mixture wasprepared by the strong acid hydrolysis method by:

1) mixing materials containing cellulose and hemicellulose with asolution of approximately 25-90% of H₂ SO₄, by weight, thereby at leastpartially decrystallizing the biomass and forming a gel that includes asolid and liquid portion;

2) diluting the gel thus obtained to an acid concentration ofapproximately 20-30% by weight and heating the gel to about 80-100° C.,thereby hydrolyzing the cellulose and hemicellulose materials (firsthydrolysis step);

3) separating the liquid portion from the solid portion, therebyobtaining a first liquid containing a sugar/acid mixture;

4) mixing the separated solid portion with a solution of about 25-90% H₂SO₄ by weight until the acid concentration of the resulting gel isbetween 20-30% by weight, and then heating the mixture to temperature of80-100° C., thereby further hydrolyzing the cellulose and hemicellulosematerials remaining in the separated solid portion (second hydrolysisstep);

5) separating the resultant liquid portion from the solid portionthereby obtaining a second liquid containing a sugar/acid mixture;

6) heating this second liquid mixture at a temperature of approximately80-120° C. for about 7-42 hours, depending on the desired product ratio,thereby forming primarily levulinic acid, 5-HMF, furfural, succinicacid, maleic acid, and fumaric acid;

7) separating this resulting third liquid, containing levulinic acid,5-HMF, furfural, succinic acid, maleic acid, and fumaric acid, from thesolid portion.

8) treating the first liquid stream with heat at approximately 80-120°C., preferably at 100° C., for about 7-24 hours, depending on thedesired product ratio;

9) the reaction mixture now contains levulinic acid, 5-HMF, furfural,succinic acid, maleic acid, and fumaric acid, which is then combinedwith the third liquid containing the similar products thereby forming asingle product stream;

10) the resultant product stream is then separated into component liquidstreams containing the desired combinations of products or theindividual components, and a separate stream containing sulfuric acid,as detailed in the above Product Flow Diagram;

11) the organic products are concentrated by removal of H₂ O, andpurified to remove residual inorganic acid and minor impurities byadjusting the pH with lime, in the case of H₂ SO₄ removing SO₄ ⁻² ions.

EXAMPLE 3 Production of Levulinic Acid

In this example, the raw materials consist of only cellulose. Thisexample is modification of examples 1 and 2 in which a solution oflevulinic acid is first prepared by mixing material containing cellulosewith a solution of sulfuric acid that is 25-90% acid by weight. Thisinitial step allows for partial decrystallization of the cellulosicmaterials.

A gel is then formed that includes a liquid and solid portion. Next thegel is diluted to yield an sulfuric acid concentration of about 20-30%by weight. The gel is then heated to a temperature between 80-100° C.for a time interval of 45 minutes to 2 hours. This step hydrolyses thecellulose.

The liquid is further heated at temperature ranging from 80-120° C. forapproximately 7-42 hours, depending on the desired product ratio. Twoportions again form: a liquid portion and a solid portion. The primaryproduct of this reaction, however, is levulinic acid, which is containedin the final liquid portion following the reaction.

The product stream is then separated into component liquid streamscontaining the desired combination of products, or the individualcomponents. The inorganic acid is contained in a separate stream. Finalpurification of the organic products is performed as outlined in theabove Product Flow Diagram.

EXAMPLE 4 Production of Levulinic Acid

700 grams of hydrolysate solution obtained from strong acid hydrolysismethod detailed in example 1, which contained 15.5% sugars, mostlyconsisting of glucose, was heated for various times at 100° C. Afterseven hours, the reaction mixture contained 3.95% of levulinic acid.

EXAMPLE 5 Production of Levulinic Acid

120 gallons of hydrolysate from strong acid hydrolysis process, asdescribed in example 1, containing approximately 1% by weight of glucoseand residual degradation products of xylose, was placed in an acidconcentrator to remove the residual H₂ O and concentrate the acid. Afterreacting at 100° C. for 24 hours, the reaction mixture was found tocontain 0.3% levulinic acid. This example demonstrates the feasibilityof producing levulinic acid as part of the routine acid recovery step inthe strong acid hydrolysis process, given that the solution containsresidual sugar.

EXAMPLE 6 Production of Esters of Levulinic Acid

It is possible to recover levulinic acid esters directly from thecompleted reaction as described in example 1. In this case, excessmethyl or ethyl alcohol, that is, in stoichiometric excess to the amountof levulinic acid produced after the reactor step (see Product FlowDiagram), can be added to the levulinic acid/sulfuric acid mixture. Theresulting mixture is refluxed for 3 hours forming the ester. The excessalcohol can then be distilled off the levulinate product. The levulinateester can be recovered by phase separation, since it forms an oily layeratop of the aqueous layer. The ester product can also be separated fromthe sulfuric acid component, as well as from the excess alcohol, by theseparation methods used for the levulinic acid product described above.

The following is example leading to the production of levulinate ester:

368 grams of a completed reaction solution from hydrolysate was used toform levulinate ester. In this case, the solution containedapproximately 15.5 grams of levulinic acid and 110 grams of H₂ SO₄. Nextethanol was added in excess. The resulting mixture was heated to ethanolreflux, approximately 80° C., for 3 hours. Following removal of the H₂SO₄ by chromatography, and removal of the remaining ethanol bydistillation, approximately 15 grams of levulinate ester was recovered.

EXAMPLE 7 Production of MTHF

After the dehydration reaction of heating the sugars in concentratedsulfuric acid, as detailed example 1, the reaction mixture is then readyto be separated as illustrated in the Product Flow Diagram. Thechromatographic separation is controlled to remove the sulfuric acid,and any of the succinic, maleic and fumaric acids that are produced inthe dehydration reaction, while leaving the remaining products oflevulinic acid, furfural and 5-HMF in a common aqueous solution. Thisaqueous solution is then concentrated by removal of H₂ O.

Next the mixture is heated at approximately 150-175° C. under a vacuumof 1-50 mm Hg, which converts the levulinic acid to 5-methyl-2-furanone(5-M-2-F). The resulting mixture, containing 5-M-2-F, furfural, and5-HMF into the hydrogenation reactor. Additionally, an ethanol solutionin water, approximately 70-95% ethanol, is added to the hydrogenatorreactor.

Water/ethanol is frequently used in hydrogenation reactions. In thisexample, the interaction of the MTHF product with ethanol allow for morefacile drying and provides the product blended with solvent. The mainreason, however, for the inclusion of ethanol in the hydrogenationreaction is that the MTHF product is highly flammable and known toproduce explosive peroxides. This high volatile nature of MTHF does notgenerally permit it to be used or shipped without the addition of aninhibitor, such as butylated hydroxytoluene. In the disclosedhydrogenation reaction, inclusion of ethanol in the reaction, greatlyreduces the risk of explosion associated with the production and use ofMTHF product. Additionally, by the inclusion of ethanol in the entireprocess, including drying of the product, the risk of explosion furtherreduced.

The mixture is reacted with H₂ in the reactor in the presence of asuitable catalyst, preferably a Co/Ni catalyst. Hydrogen is added at anexcess pressure of 750-3000 psig until there is no further H₂ uptake.Any residual H₂ O is removed by azeotropic distillation or molecularsieve drying. The resulting product is an ethanol-MTHF blend which isready for use or can be further separated into its two components.

It should be noted that although furfural can be hydrogenated in thepresence of a Ni/Co catalyst, it is more difficult to hydrogenate than5-HMF or 5-M-2-F. Thus, at the conditions specified for hydrogenationreaction of levulinic acid in the present invention, the entire mixturewill be hydrogenated to yield MTHF. Moreover, the conditions forproducing MTHF need to be selected for optimization of the reaction. Iftoo much hydrogen pressure, or too high a temperature, is used, thereaction may go pass MTHF to yield 1,4-pentanediol instead.

EXAMPLE 8 Production of MTHF

The process of Example 7 is performed with the addition of dry ethanolrather than aqueous ethanol.

EXAMPLE 9 Production of MTHF

The process of Example 7 in which no ethanol is added to thehydrogenation reactor. In this example, the hydrogen pressure in thehydrogenation step is increased to approximately 2000-5000 psig.

After Sugar/Acid Separation

After the sugar and acid have been separated, which can be done afterthe first hydrolysis step, or after the second, the remainingconcentration of acid is approximately 1%. This acid can either be leftin the sugar mixture, or the acid can be converted to a salt which maybe a suitable catalyst for the next chemical conversion, depending onthe chemical route chosen.

Examples of additional chemical reactions that can be accomplished onthe sugars after separation from the inorganic acid componentinclude: 1) neutralization of the acid with sodium sulfate followed byelectrolytic reduction to polyols; 2) air oxidation in the presence ofsulfuric acid leading to difunctional acidic sugars; 3) neutralizationof the sugar/acid mixture to a pH of 9.5-10.0 followed by air oxidationto monofunctional acidic sugars.

In is important that in both experimental approaches, either using thehydrolysate immediately after pressing, or by first putting thehydrolysate through the acid/sugar separation process, the criticalpurifications would be delayed until the value of the desired productsare at their highest value for recovery. Thus, purification can bedelayed until the production of the final products. If needed, aninitial separation and purification of final products can beaccomplished by the separation method described in the Product FlowDiagram of FIG. 1. Final purifications steps can be achieved in theconventional manner.

Exemplary Method of Production of Levulinic Acid by the IntegratedProcess

The following examples sets forth the techniques to produce levulinicacid and other products from a cellulose and hemicellulose materialwherein the sugar or sugar/acid stream is not recovered as anintermediate. Although these methods are presented here, the levulinicacid produced by this method may be used in any of the proceduresdescribed herein which use levulinic acid to form other products.

EXAMPLE 10 Production of Levulinic Acid

A mixture of papers, predominantly newspaper but containing smallamounts of plastic, glossy paper and cardboard, with a cellulose contentof 85% was chosen as the raw material. Paper was added slowly to asolution of sulfuric acid in a 20 gallon glass-lined pressure vessel soas to keep the temperature of the mixture at or below about 40° C. Thismay also be accomplished by cooling the reaction vessel, or by acombination of slow addition and cooling. The concentration of sulfuricacid in the final solution was 10% by weight and the concentration ofthe cellulose by weight in the reaction solution was 25.5% (30% paper byweight).

After about 1.5 hours, the decrystallization was complete, and themixture was then heated. It took approximately one hour to heat themixture to the reaction temperature of 150° C. The time to achieve thereaction temperature is a function of the equipment and quantitiesinvolved; it is not a critical parameter in the process. Once themixture was at the reaction temperature, the temperature was maintainedfor 8 hours. The mixture was then filtered to remove the solids and theproduct stream separated into component liquid streams, as outlined inthe Product Flow Diagram above. The reaction produced 10.9% levulinicacid or 59.8% of the theoretical yield of levulinic acid from thequantity of cellulose in the paper.

EXAMPLE 11 Production of MTHF

The process of Example 7 was performed, using the reaction mixture fromExample 10 in place of the mixture from Example 1. Examples 8 and 9 canalso be performed similarly.

EXAMPLE 12 Production of Esters of Levulinic Acid

This method proceeds like that in Example 6, except the procedure ofExample 10 is used to produce levulinic acid is performed and themixture is filtered. Excess methyl or ethyl alcohol, that is, astoichiometric excess to the amount of levulinic acid produced, can beadded to the levulinic acid/sulfuric acid mixture. The resulting mixtureis refluxed for about 3 hours forming the ester. The excess alcohol canthen be distilled off the levulinate product. The levulinate ester canbe recovered by phase separation, since it forms an oily layer atop ofthe aqueous layer. The ester product can also be separated from thesulfuric acid component, as well as from the excess alcohol, by theseparation methods used for the levulinic acid product described above.

Exemplary Methods of Production of Levulinic Acid from Sugars

The following examples set forth specific techniques of the productionof levulinic acid from different sugar mixtures:

EXAMPLE 13

The solution of 3% xylose, 12% glucose and 30% sulfuric acid was heatedfor various times at 100° C. The quantity of the total reactants was 500grams. After 7 hours there was no sugar left and the levulinic acidconcentration was 1.1%. By 16 hours, the levulinic acid had increased to2.6%; and at 24 hours, the levulinic acid concentration was 4.2%. Thefinal absolute yield of levulinic acid was 35% or 54% of the theoreticalyield.

EXAMPLE 14

A solution of 12% glucose, by weight, and 30% H₂ SO₄, by weight, washeated for various times at 100° C.±5° C. After 3 hours no significantlevulinic acid was formed, however, the sugar had degraded to 4.49%along with significant production of 5-HMF. After 4 hours, the levulinicacid production was only 0.18% while the sugar had been reduced byapproximately one-half of the 3 hour point. After a 7 hour reactiontime, levulinic acid production was approximately 2.33%, and the sugarwas reduced only slightly further. After 24 hours, there was notmeasurable sugar left, and the levulinic acid was now at 2.95%, or 46%of the theoretical yield.

Hydrogenation Reaction Leading to MTHF: Preparation of the MetalCatalyst

A typical hydrogenation catalyst can be prepared from Fe, Cu, Mn, Co, orNi. Preferably, a mixture of Ni/Co can be used as the catalyst forhydrogenation of levulinic acid. The substrates for the catalyst can bechosen form alumina (Al₂ O₃), magnesia (MgO) or zirconia (ZrO₂).Moreover, these substrates can be impure, thus the highest grade metalsubstrate is not required for the production of the hydrogenationcatalyst.

If using a salt of any of the transition metal catalysts, these saltscan be dissolved in ethanol or methanol. The substrate is also immersedin the solution, and then, removed and dried. This dried matrix,containing both the catalyst and substrate, is then placed in a kiln,and heated to 850-1000° C., for at least 30 minutes, followed by coolingbefore use in the hydrogenation reaction. If the catalysts becomedeactivated by the cooling process, they can be regenerated by reheatingat 850-1000° C.

For each catalyst particle size, surface concentration of metal oxidespecies, ratio of catalyst used to reactor size, reactor volumes andtemperatures, there will be a specific hydrogen pressure which willoptimize the yield of MTHF without conversion of significant quantitiesof MTHF to 1,4-pentanediol. The other major constraint is temperature atthe hydrogenation step. Excess temperatures can cause degradation ofboth starting products and lead to degradation of the desired endproduct. Generally it is preferred that the reactor temperature does notexceed 200° C.

EXAMPLE 15

As an example of the preparation of a catalyst for the hydrogenationreaction of levulinic acid to MTHF, 1-15 grams of Ni or Co acetate wasdissolved in 40-50 ml of ethanol or methanol. 80-100 grams of roughlyspherical alumina or zirconia particles of approximate diameter of 1/4"diameter were placed in the liquid, removed, and dried for about 4 hoursat 105° C. The particles were then placed in a kiln, which is heated to850° C. (this heating step took 1.5 hours). The pellets were held at, orabove, this temperature for 30 minutes, cooled and removed for use.

EXAMPLE 16

1 gram of copper acetate was placed in 40 ml of ethanol and 80 grams ofZrO₂ of roughly 1/4" spheres was added. The ZrO₂ /CuOAc was dried for 4hours at 105° C. The mixture was then placed in a kiln and heated up to850° C., where it was held at this temperature for 30 minutes.

The purpose of the heating step above is to convert the acetate salts tooxides which become bound to the substrate surface. The acetate saltsform only CO₂ and water upon heating. However, although nitrate saltscan be used for this process, these salts form toxic NO₂ instead upondecomposition, and thus, are less preferred.

What is claimed is:
 1. A method of producing levulinic acidcomprising:mixing biomass containing cellulose and hemicellulose with anacid to form an aqueous reaction solution which is 5-50% acid by weightwhile maintaining the temperature of the solution below about 60° C.,thereby at least partially decrystallizing the biomass; heating saidsolution to about 80-200° C. for 1 to 30 hours, thereby hydrolyzing thecellulose and hemicellulose materials to sugars which are reactedfollowing hydrolysis; separating the reaction products; and recoveringlevulinic acid.
 2. The method of claim 1, wherein the acid is sulfuricacid.
 3. The method of claim 1, wherein the concentration of saidbiomass is about 20-40% by weight in the reaction solution.
 4. Themethod of claim 1, wherein the concentration of said biomass is about30% by weight in the reaction solution.
 5. The method of claim 1,wherein the concentration of cellulose is about 12-39% by weight in thereaction solution.
 6. The method of claim 1, wherein the concentrationof cellulose is about 21-30% by weight in the reaction solution.
 7. Themethod of claim 1, wherein said biomass comprises rice straw materials.8. The method of claim 1, wherein said biomass comprises woody plantmaterials.
 9. The method of claim 1, wherein said biomass comprisespaper materials.
 10. The method of claim 1, wherein said biomasscomprises cotton material.
 11. The method of claim 1, wherein saidbiomass comprise cellulosic materials.
 12. The method of claim 1,wherein said biomass comprises corn stalks.
 13. The method of claim 1,wherein said biomass comprises bagasse.
 14. The method of claim 1,wherein the step of heating said solution is conducted at 110-160° C.15. The method of claim 1, wherein the concentration of the acid in thesolution is about 10-30%.
 16. The method of claim 1, wherein the step ofheating the solution is conducted for 2 to 10 hours.
 17. The method ofclaim 1, wherein the concentration of cellulose, the concentration ofthe acid and the temperature of the heating step are determinedaccording to the equation:

    A=0.4T+70-0.59(C-25.5);

wherein A is the percent sulfuric acid by weight in the reactionsolution, T is the temperature in degrees Celsius, and C is the percentcellulose by weight in the reaction solution; and wherein the conditionsused deviate from those obtained from the equation by not more than 5%by weight in the reaction solution for the value obtained for A, notmore than 5% by weight in the reaction solution for the value obtainedfor C, and not more than 10° C. of the value obtained for T.
 18. Themethod of claim 17, wherein the concentration of cellulose is 12-39% byweight in the reaction solution.
 19. The method of claim 1, additionallycomprising recovering a product selected from the group consisting offurfural, 5-HMF, succinic acid, maleic acid and fumaric acid.
 20. Themethod of claim 1, wherein said product recovered is furfural.
 21. Themethod of claim 1, wherein said products recovered is furfural and5-HMF.
 22. The method of claim 1, wherein the step of separating theproducts comprises chromatography.
 23. The method of claim 1, whereinstep of separating the products comprises chromatography using an ionicresin.
 24. The method of claim 1, wherein step of separating theproducts comprises chromatography using an anionic resin.
 25. The methodof claim 1, wherein step of separating the products compriseschromatography using a multiple chromatographic columns.
 26. The methodof claim 1, additionally comprising:hydrogenation of levulinic acid thusobtained in the presence of H₂ and a metal catalyst; separating thereaction products; and recovering methyltetrahydrofuran.
 27. The methodof claim 26, wherein ethanol is added during the hydrogenation step. 28.The method of claim 26, wherein the methyltetrahydrofuran is dried afterthe hydrogenation reaction, leaving a methyltetrahydrofuran product in adry blend form.
 29. The method of claim 26, wherein dry ethanol isadded.
 30. The method of claim 26, wherein the metal catalyst is Ni/Cocatalyst.
 31. The method of claim 1, additionally comprising dehydrationof levulinic acid to yield a product comprising an angelica lactone. 32.The method of claim 1, additionally comprising filtering the reactionproducts prior to separation.
 33. The method of claim 32, wherein thefilter is washed with H₂ O.
 34. The method of claim 32, wherein both thefirst filtrate and second filtrate following the H₂ O washed arecombined before separation.
 35. The method of claim 1, wherein levulinicacid is concentrated after separation and recovery.
 36. The method ofclaim 1, additionally comprising:adding an alcohol to the levulinicacid; refluxing the resulting alcoholic solution for 1-10 hours;separating the mixture; recovering levulinate ester.
 37. The method ofclaim 36, wherein the reaction mixture is refluxed for 2-8 hours. 38.The method of claim 36, wherein the reaction mixture is refluxed for 3-6hours.